I am a long backed, short legged 6 footer, and I do lot of long distance riding and have ridden most of the major sports touring bikes FJR, ST1100, 1300, and other bikes from the multistrada and KTM 950 but two of my rides stood out for comfort--a '99 BMW 650 GS and an Aprilia Maxi scooter (Scarabeo 500). Both had relaxed seating but had room to move my legs. Sports bikes are great for up to 5-6 hours= R1, R6, YFr 600, Super Hawk and so on but a fixed leg position kills us over time. The semi enduros make great commuters too. The back pain you suffer comes from two aspects of riding. The straight up and down position with your weight on your butt, and the other comes from slumping and letting your back muscles sag. Any ride that has you leaning forward a little with some of your weight supported by your legs helps combat the back ache. All the bikes posted should suit you just fine, but do look at the BMWs.